MSA vs. Measurement Capability Analysis - What are the differences?

Hello people,

Just want to know about the difference between MSA and Measurement Capability Analysis? Hope to hear your reply.

Thanks!
Errol

Measurement capability analysis and MSA are one and the same.

errolreyes said:

Just want to know about the difference between MSA and Measurement Capability Analysis? Hope to hear your reply.

Click to expand...

Welcome to the Cove, Errol!

Yes, they are basically the same. The whole exercise of MSA helps you quantify the two types of variation (position variation - bias, linearity and width variation-GRR) for measuring a particular characteristic.

Various indexes can be computed.

A. Based on a Bias/Repeatability Study

(Ref: My old notes based on the booklet "Capability of Measuring Instruments": Robert Bosch)
Take repeated measurements (25-50) on a production master, calculate average and Repeatability StDev.

The two indexes calculated are:
1. Cgm = (0.2 * Tolerance) / (6 * Rpt_Stdev)
2. Cgmk = Least of
( RefValue + (0.1 * Tolerance) - XBar) / (3 * Rpt_StDev)
-OR-
( XBar - (RefValue - (0.1 * Tolerance)) ) / (3 * Rpt_StDev)

Both should be >= 1.33; and bias (XBar-RefValue) not significant.

B. Based on GRR, typically two indexes are recommended:

1. Measurement Capability Index (MCI_I) based on Process Variation is defined as:
MCI_I = 100 (Sigma_GRR/Sigma_process)
Sigma_Process is calculated from ongoing SPC studies: RBar/d2

2. The other index, (MCI_II) is based on tolerance:
MCI_II = 100 (5.15 * Sigma_GRR/ Tolerance )
In place of 5.15 you can also use 6 to cover 99.73% spread.

Acceptance criteria for both these are:
<=20% :Good
>20 - <=30% :Marginal
>30% :Unacceptable

MSA vs Measurement Capability Analysis-what the differences ?

Thank you so much for your replies.It's help me a lot

Actual GR&R Constant ?

Found that the Constant for GR&R shown on the example in page 114 of MSA 3rd edition is not same as the sample shown in SPC manual.

i.e Trial (3) k1 = 0.5908 in MSA manual but in SPC manual
Trial (3) K1 = 3.05 .

Is there a reason for this. Am i missing something big ?

Need help !!! Spiderman, Superman , Super-Consultant..

Thanks and Regards.

The constants changed between the 2nd and 3rd edition of MSA.
I am afraid that I cannot explain the statistics but the effect is supposed to be minor.

Thanks for the reply howard.

The new constant stated in the MSA 3rd edition. Which page is this. Sorry to ask but im really confused and cant find it.

Thanks and regards.

You've already found it--it's the form you referred to in an earlier post, on page 114 of the MSA manual.

Wow. and i thought that's an example only. And there'll be the actual constant in the manual somewhere in a nice table format.

Confused and dumb-founded ...

Thanks and regards.

What ever happened to the old "10:1" rule for measurement systems? Seems like MSA and other analyses are just rehashing the idea that the measurement system should not take up more than 10% of your total process variation. Where did I lose it?